1. Field of the Invention
The present invention relates to an upper and lower distortion correcting circuit by modes, and more particularly, to an upper and lower distortion correcting circuit by modes which can correct upper and lower distortion generated in a display monitor which receives and displays video signals generated by a personal computer (hereinafter referred simply to as a "PC").
2. Related Art
Generally, a display monitor receives a video signal generated by a PC body and displays the received video signal on a display screen. In more detail, the display monitor amplifies the video signal generated by the PC through a video amplifying circuit and then displays the amplified video signal as a visible image on a cathode-ray tube (hereinafter, referred to as a "CRT"). To this end, the display monitor needs a sawtooth current for synchronizing the video signal.
The sawtooth current enables horizontal and vertical synchronous signals generated by the PC to be transmitted and processed through a microcomputer within the display monitor and is generated in accordance with the periods of horizontal and vertical pulses. The horizontal and vertical pulses generated by the microcomputer are supplied to a deflection circuit and synchronize the video signal through a deflection yoke attached to a neck of the CRT, to thereby display the video signal as a visible image.
Since a display monitor is provided with an upper and lower distortion correcting circuit having a non-linearity feature, there occurs a problem in that a non-linearity current, that is, a secondary functional current, must be supplied to the correction circuit. Furthermore, there occur another problem in that the screen distortion correcting circuit is used only in a single mode, that is, at a single frequency, and has a fixed amount of distortion correction.